This is the 2568th most frequent German word.
wälder
Forests.
Wälder is used as the plural form of 'Wald' indicating multiple forests.
Die Wälder in Deutschland sind bekannt für ihre Schönheit.
The forests in Germany are known for their beauty.
Here, 'Wäldern' is used as the plural dative case of 'Wald', fitting the preposition 'in' which governs the dative case in this usage.
In den Wäldern leben viele verschiedene Tierarten.
In the forests live many different species of animals.
'Wälder' is in the accusative case as it is the object of the sentence.